The PM has been speaking in WA.

Prime Minister Malcolm Turnbull has thrown his weight behind the government's controversial cashless welfare trial, describing it as an "exercise in practical love".

Mandurah in Western Australia has been named the third site for the Turnbull Government's drug testing trial for welfare recipients, which will see social security payments of drug takers locked onto a dedicated card.

The government says it has seen big falls in alcohol consumption and gambling since trials began last year at trial in Ceduna, South Australia, and in WA's East Kimberley.

Speaking on Saturday, Turnbull described the rollout of the trial as a "fantastic reform".

"It has seen a massive reduction in alcohol abuse, in drug abuse, in domestic violence, in violence generally -- really huge improvements in the quality of life, not just for the families who are using the cashless welfare card, but for the whole community," he told a Liberal Party event in WA.

"But, above all, it's an investment in the future of the children ... So this is truly an exercise in practical love."

Human Services Minister Alan Tudge has previously said that Mandurah, like those sites already announced in western Sydney and Logan, Queensland, is the right place to trial the system.

Under the two-year trial, up to 5000 new recipients of Newstart Allowance and Youth Allowance will be drug tested, which is already underway in Sydney's Bankstown.

It will see those who return a positive test have 80 per cent of their benefit payment quarantined onto a Basics Card. The card limits the amount of money people can withdraw as cash due to concerns it will be spent on illicit substances.

In addition to Bankstown, the targeting of Logan in Queensland is due to the high level of welfare sign-up in the area and increasing use of ice and ice-related hospitalisations.

The Mayor of Logan City, Luke Smith, has previously complained bitterly he was not consulted, but the coalition says it was a federal program there was no need for local consultation.